The present invention relates to appliance construction in general and in particular to a construction for a dishwasher using gas injection plastic molding techniques.
Gas injection molding techniques are generally known such as described in U.S. Pat. No. 5,401,459. Gas injection molding can generally be described as a process where gas is injected into a plastic mold which holds hot plastic in order to totally fill the mold cavity thereby providing a plastic part that is hollow. For example, if the technique is applied to the creation of a tube, the mold may consist of a cavity that would ordinarily produce a solid bar. The tube is first injected with hot plastic, in an amount less than enough to fill the cavity. This amount is normally referred to as a "short shot." If a solid bar was in fact desired, this short shot would result in an incomplete and defective part. In the case of gas injection molding however, the short shot would be followed with an injection of an inert gas at high pressure. The plastic would have just begun to cool slightly at the outer edges such that the gas will blow the center of the plastic along the mold, causing the mold to fill to the end with a hole through the center of the hollow tube.
A typical dishwasher includes a tub for enclosing the dish containing-and washing area. Conventionally, the tub is made of sheet metal, however a tub of molded plastic material such as polypropylene is disclosed in U.S. Pat. No. 5,230,553. The tub disclosed in this patent is reinforced around an outer circumference thereof with rib like members. For dishwashers which employ an upper spray arm, a water conduit must be provided from the wash water pump to the elevated, upper spray arm. Particularly, many current designs use a short extension directly vertically arranged above the pump which sprays water vertically through the rack area in what is referred to as a "tower." The tower is clearly visible inside the dishwasher and reduces the useful area inside the dishwasher.
It is also possible to fabricate a wash water feed tube from the wash water pump to the upper arm inside the tub. However, although external leaks will be prevented or contained, the inside of the tub becomes somewhat more restricted. These tubes also provide areas where food particles can become trapped and not easily removed from the system. The tube inside the tub also gives the appearance of an unappealing necessity. U.S. Pat. No. 3,082,779 describes a tub assembly made of metal and having on an inside surface thereof a conduit for feeding water to an upper spray tube.
Also, upper arm water feed can be provided with a separate tube passing along the outside of the tub. Connections must be made between the tube and the pump and the upper wash arm, adding labor costs. Also, being outside the tub, the chance of water leaks at the connections and the drawbacks of such water leaks is increased dramatically.